Apparatus and method for automatically compensating for lateral runout

ABSTRACT

An apparatus and method for automatically compensating for the lateral runout between an on-car lathe apparatus and a vehicle hub axis including one or more stop discs that rotate with the drive shaft of the lathe and that can be selectively stopped from rotating with the shaft by a stop mechanism. In response to such stopping, one or more adjustment discs are caused to rotate in order to adjust the relative position of the axis of the lathe with respect to the axis of the disc brake assembly. In this manner, the system compensates for and corrects lateral runout that exists between two concentrically attached rotating shafts.

BACKGROUND OF THE INVENTION

This invention relates to an improved on-car brake lathe apparatus. Morespecifically, this invention relates to an apparatus and method forautomatically compensating for the lateral runout of a lathe apparatuswith respect to a vehicle hub. The invention further includes a novelrunout measurement and control system that describes the runout of adisc brake assembly and directs a corrective signal to an automatedcontrol system for adjustment in order to effectively compensate oflateral runout. The novel runout apparatus and method may also b)eadvantageously utilized in other practical applications in order toalign two concentrically attached rotating shafts.

A brake system is one of the primary safety features in every roadvehicle. The ability to quickly decelerate and bring a vehicle to acontrolled stop is always critical to the safety of the vehicleoccupants and those in the immediate vicinity. In this, a vehiclebraking system is designed and manufactured to exacting specificationsand rigorous inspection.

One of the main components of a brake system are the disc brakeassemblies typically mounted on the front wheels of most passengervehicles. Generally, the disc brake assemblies include a caliper(cooperating with a brake hydraulic system), brake pads, a hub, and arotor. The caliper supports and positions a pair of brake pads onopposing sides of a brake rotor. In a hubless brake rotor (i.e. when therotor and hub are separate components), the rotor is secured to thevehicle hub, via a rotor hat, with a series of bolts for rotation withthe hub about a vehicle spindle axis. When a vehicle driver depresses abrake pedal thereby activating the hydraulic system, the brake pads areforced together and toward the rotor to grip the friction surfaces ofthe rotor.

Disc brake assemblies must be maintained to manufacturers specificationsthroughout the life of the vehicle in order to assure optimumperformance and maximum safety. However, several problems have plaguedthe automotive industry since the inception of disc brakes.

A significant problem in brake systems is usually referred to as"lateral runout." Generally, lateral runout is the side-to-side movementof the friction surfaces of the rotor as it rotates with the vehicle hubabout a spindle axis. Referring to FIG. 1, for example, there is shown arotor having friction surfaces on its lateral sides. A rotor is mountedon a vehicle hub for rotation about the horizontal spindle axis X. In anoptimum rotor configuration, the rotor is mounted to rotate in a plane Ythat is precisely perpendicular to the spindle axis X. Generally, goodbraking performance is dependant upon the rotor friction surfaces beingperpendicular to the spindle's axis of rotation X and parallel to oneanother ("parallelism"). In the optimum configuration, the opposingbrake pads will contact the friction surfaces of the rotor at perfect 90degree angles and will exert equal pressure on the rotor as it rotates.More typically, however, the disc brake assembly will produce at least adegree of lateral runout that deviates from the ideal configuration. Forexample, a rotor will often rotate in a canted plane Y' and about anaxis X' which is a few thousandths of an inch out of axial alignmentwith the spindle (shown in exaggerated fashion in FIG. 1). In this rotor(configuration, the brake pads, which are perpendicular to the spindleaxis X, will not contact the friction surfaces of the rotor along aconstant pressure plane.

The lateral runout of a rotor is the lateral distance that the rotordeviates from the ideal plane of rotation Y during a rotation cycle ofthe rotor. A certain amount of lateral runout is inherently present inthe hub and rotor assembly. This lateral runout often results fromdefects in individual components. For example, rotor friction surfacerunout results when the rotor friction surfaces are not perpendicular tothe rotor's own axis of rotation, rotor hat runout results when the hatconnection contains deviations that produce an off center mount, andstacked runout results when the runouts of the components are added or"stacked" with each other. An excessive amount of lateral runout in acomponent or in the assembly (i.e. stacked runout) will generally resultin brake noise, pedal pulsation, and a significant reduction in overallbrake system efficiency. Moreover, brake pad wear is uneven andaccelerated with the presence of lateral runout. Typically,manufacturers specify a maximum lateral runout for the frictionsurfaces, rotor hat, and hub that is acceptable for safe and reliableoperation.

After extended use, a brake rotor must be resurfaced in order to bringthe brake assembly within manufacturers specifications. This resurfacingis typically accomplished through a grinding or cutting operation.Several prior art brake lathes have been used to resurface brake rotors.These prior art lathes can be categorized into three general classes:(1) bench mounted lathes; (2) on-car caliper-mounted lathes; and (3)on-car hub mounted lathes. As discussed below, the on-car hub mountedlathes have proven to be the most reliable and accurate rotorrefinishing lathes in the industry.

Bench mounted lathes, for example, that disclosed in U.S. Pat. No.3,540,165 to Lanham, are inefficient and do not have rotor matchingcapabilities. In order to resurface a rotor on a bench mounted lathe,the operator is first required to completely remove the rotor from thehub assembly. The operator then mounts the rotor on the bench latheusing a series of cones or adapters. After the cutting operation, theoperator remounts the rotor on the vehicle spindle. Even if the rotor ismounted to the lathe in a perfectly centered and runout free manner,runout between the rotor and hub is not accounted for in the bench latheresurfacing operation. In addition, bench lathes are susceptible to bentshaft, which introduce runout into a machined rotor. This runout is thencarried back to the brake assembly where it may be added with hub runoutto produced a stacked runout effect.

Similarly, caliper-mounted lathes, for example, that disclosed in U.S.Pat. No. 4,388,846 to Kopecko et al., have had limited success incompensating for lateral runout, but require time consuming manualoperations. During a rotor refinishing procedure, the brake caliper mustfirst be removed in order to expose the rotor and hub. Once removed, thecaliper mounting bracket is freed and can be used to mount an on-carcaliper-mount lathe. The caliper-mount lathes are wholly unacceptablefor many reasons including the lack of a "rigid loop" connection betweenthe driving motor and cutting tool and the inability to assure aperpendicular relationship between the cutting tools and the rotor.Moreover, the caliper-mount lathes do not have any reliable means formeasuring and correcting lateral runout. Typically and in much the samemanner as described below with reference to the hub mounted lathes, adial indicator is utilized in determining the total amount of lateralrunout in the disc assembly. This measurement technique is problematicin terms of time, accuracy and ability of automechanics to comfortablyuse the equipment.

On-car hub mounted lathes, for example, that disclosed in U.S. Pat. No.4,226,146 to Ekman, assigned to the assignee of the instant application,and incorporated by reference into the disclosure herein, have proven tobe the most accurate and efficient means for resurfacing the rotor.

Referring now to FIG. 2, there is shown an Ekman type on-car disc brakelathe 10 for mounting to the hub of a vehicle 14. The lathe 10 includesa body 16, driving motor 18, adapter 20, and cutting assembly 22. Thelathe is also provided with a stand and anti-rotation post (not shown),either of which can be used to counter the rotation of the lathe duringa resurfacing operation. After the brake caliper is removed, the adapter20 is secured to the hub of the vehicle 14 by using the wheel lug nuts.The lathe body 16 is then mounted to the adapter 20.

At this point in the prior art procedure, the operator must determinethe total amount of lateral runout and make an appropriate adjustment.Specifically, the operator first mounts a dial indicator 26 to thecutting head 22 using ai knob 28. The dial indicator 26 is positioned tocontact the vehicle 14 at one of its distal ends as shown in FIG. 2.Once the gauge 26 is properly positioned, the operator is required totake the following steps in order to measure and compensate for lateralrunout:

(1) The operator mates the lathe to the rotor using the adapter andprocedure outlined above.

(2) The operator activates the lathe motor 18 which causes the adapter20, and thereby the brake assembly hub and rotor, to rotate. The totallateral runout of the assembly will be reflected by correspondinglateral movement in the lathe body.

(3) The lateral movement of the lathe body is then quantified by usingthe gauge 26. Specifically, the operator observes the dial indicator todetermine the high and low deflection points and the correspondinglocation of these points on the lathe.

(4) Upon identifying the highest deflection of the dial indicator, theoperator "bumps" the motor and stops the rotation at the point of theidentified highest deflection.

(5) The operator then makes an adjustment to compensate for runout ofthe assembly. This is accomplished by careful turning of the adjustmentscrews 24. Specifically, there are four adjustment screws and thecorrect screw(s) must be turned depending on the location of the highpoint. The affect of turning the screws is to adjust the orientation ofthe lathe body with respect to the adapter 20 (and therefore the rotorand hub) to mechanically compensate for the runout of the assembly. Theoperator adjusts the screws until the highest deflection point isreduced by half as determined by reference to the dial indicator 26.

(6) The operator activates the lathe motor 18 and observes the dialindicator 26 to again identify the highest deflection of the dial. Ifthe maximum lateral movement of the lathe body, as measured by theneedle deflection, is acceptable (i.e. typically less than 3/1000) thenmechanical compensation is complete and the lathe turning operation cancommence. Otherwise, further measurement and adjustment will benecessary by repeating steps (1) to (6).

The cutting operation is then performed by adjusting the tool holder 22and cutting tools 23, and setting the proper cutting depth.

Although the hub mounted on-car brake(lathe was a considerable advancein the disc brake lathe industry, its structure and correspondingprocedure for compensating for lateral runout of the disc brake assemblyhas practical limitations.

First, as readily apparent, upon observation of steps (1)-(6) above, theEkman procedure requires a significant amount of time to determine andadjust for lateral runout of the brake assembly. Although the specificamount of time necessary will vary based upon operator experience, theprocedure time for even the most trained and experience is significantand can substantially increase the cost associated with rotorrefinishing to the vehicle owner and the shop. Second, the prior artsystem and procedure requires the shop owner and technicians to undergoextensive education and operator training in order to assure that propermechanical compensation for lateral runout is accomplished. Moreover,the Ekman system is operator specific. That is, the accuracy and successof measurement and adjustment of lateral runout will vary from operatorto operator.

In general, the prior art systems and procedures are problematic withrespect to accuracy in the measuring and adjusting of lateral runout.The prior art systems require an operator to locate a high reading forlateral runout by viewing the gauge 26; often, the operator is requiredto "bump" the motor to relocate the high point once it has beenidentified. Moreover, even if the operator correctly locates and/orrelocates the high point of lateral runout, human errors are oftenintroduced during the adjustment process. For example, selecting thecorrect screw or screws 24 and applying the precise amount of torquenecessary for adjustment is often difficult and imprecise.

The difficulties and limitations suggested in the preceding are notintended to be exhaustive, but rather are among many which demonstratethat although significant attention has been devoted to disc brakelathes, such systems will admit to worthwhile improvement.

OBJECTS AND BRIEF SUMMARY OF THE INVENTION

It is therefore a general object of the invention to provide a novelon-car disc brake lathe system which will obviate or minimizedifficulties of the type previously described.

It is another general object of the invention to provide a novel runoutmeasurement and control system for an on-car disc brake lathe thataccurately detects and quantifies the runout of a lathe apparatus withrespect to a vehicle hub assembly.

It is yet another general object of the invention to provide a novelautomated alignment apparatus for an on-car disc brake lathe thatadjusts the axial alignment of the lathe in accordance with informationproduced by a runout sensing and control system.

It is a specific object of the invention to provide a novel runoutmeasurement and control system for an on-car disc brake lathe thatdirects a corrective signal to an automated control system foradjustment.

It is a specific object of the invention to provide a novel on-car discbrake lathe apparatus which eliminates the need for manual adjustment byan operator in order to compensate for lateral runout.

It is another specific object of the invention to provide a novel on-cardisc brake lathe apparatus system which will accurately and consistentlymeasure and adjust for runout.

It is still another specific object of the invention to provide a novelon-car disc brake lathe apparatus which will significantly reduce thetime required for a complete brake disc lathing operation.

It is still yet another specific object of the invention to provide arunout measurement and control system for an on-car disc brake lathehaving a processing unit for accurate and reliable data evaluation.

It is another specific object of the invention to provide a runoutmeasurement and control system for an on-car disc brake lathe thatadvises in operator or directs an electrically controlled system toperform an axial alignment of the lathe and vehicle hub.

It is still another specific object of the invention to provide anautomated alignment device for an on-car disc brake lathe thataccurately adjusts the relative angle between the vehicle hub's axis ofrotation and the lathe's drive shaft.

It is yet another specific object of the invention to provide anautomated alignment apparatus for an on-car disc brake lathe that, whenused with a suitable control system, will reduce the total lateralrunout of the lathe with respect to the vehicle hub assembly to withinacceptable manufacturing specifications.

It is further specific object of the invention to provide an automatedalignment apparatus for an on-car disc brake lathe that is simple,accurate, capable of computer control, and low in cost.

It is another specific object of the invention to provide a runoutmeasurement and control system for an on-car disc brake lathe thatsenses rotational accelerations while rejecting linear accelerations inany of the three dimensional axes.

It is another specific object of the invention to provide a runoutmeasurement and control system for an on-car disc brake lathe thatsenses rotational that it is a one piece mechanism mounted securely tothe lathe and not subject to operator error during setup.

SUMMARY OF THE INVENTION

The automatic alignment apparatus for an on-car disc brake lathe of thepresent invention which is intended to accomplish at least the foregoingobjects includes a brake lathe having an automatic alignment couplingthat operates in response to cl corrective signal to adjust thealignment of the lathe with respect to the vehicle in order tomechanically compensate for lateral runout. The automatic alignmentmechanism includes one or more stop discs that rotate with the driveshaft of the lathe and that can be selectively stopped from rotatingwith the shaft by a stop mechanism. In response to such stopping, one ormore adjustment discs are caused to rotate in order to adjust therelative position of the axis of the lathe with respect to the axis ofthe disc brake assembly. In this manner, the system compensates for andcorrects lateral runout that exists between two concentrically attachedrotating shafts.

DRAWINGS

Other objects and advantages of the present invention will becomeapparent from the following detailed description of the invention, takenin conjunction with the accompanying drawings, wherein:

FIG. 1 is a graphical representation of a lateral runout phenomenon.

FIG. 2 is a plan view showing an on-car disc brake lathe and depicting aprior art procedure for measuring, and compensating for lateral runoutof a disc brake assembly.

FIG. 3 is a perspective view showing an on-car disc brake lathe mountedon the hub o: a vehicle in preparation for a disc resurfacing operationin accordance with the present invention.

FIG. 4 is a partially sectional schematic view of a disc brake lathewith an automatic alignment apparatus of the first preferred embodimentof the present invention mounted on the hub of a vehicle.

FIGS. 5a and 5b are cross-sectional and front views, respectively, ofthe automatic alignment apparatus of the first preferred embodiment ofthe present invention.

FIG. 6 is a cross-sectional view of the adjustment disc assemblies ofthe automatic alignment apparatus of the first preferred embodiment ofthe present invention.

FIGS. 7a and 7b are front cross-sectional views of one of the adjustmentdisc assemblies of the automatic alignment apparatus of the firstpreferred embodiment of the present invention.

FIGS. 8 and 9 are cross-sectional views of the adjustment discassemblies of the automatic alignment apparatus of the first preferredembodiment of the present invention.

FIGS. 10a and 10b are cross-sectional and side views, respectively, ofthe automatic alignment apparatus of the second preferred embodiment ofthe present invention.

FIGS. 10c and 10c-1 is a front and cross-sectional views, respectively,of an adjustment disc of the automatic alignment apparatus of the secondpreferred embodiment of the present invention.

FIGS. 10d and 10D1 is a front and cross-sectional views, respectively,of a slant disc of the automatic alignment apparatus of a pivot ring ofthe second preferred embodiment of the present invention.

FIGS. 11a and 11b are schematic representations of the compensationvector and compensation alignment angle of the automatic alignmentapparatus of the second preferred embodiment of the present invention.

FIG. 12 is a cross-sectional view of the automatic alignment apparatusof the third preferred embodiment of the present invention.

FIGS. 13a and 13b are front views of the input and output adaptorassemblies and a front view of the drive arm assembly, respectively, ofthe automatic alignment apparatus of the third preferred embodiment ofthe present invention.

FIG. 14 is a front view of the starwheel stop mechanism of the of theautomatic alignment apparatus of the third preferred embodiment of thepresent invention.

FIG. 15a is a timing diagram of the hall transducer timing pulse duringthe starwheel stop operation of the automatic alignment apparatus of thethird preferred embodiment of the present invention.

FIG. 15b is a timing diagram of the forward starwheel position duringthe starwheel stop operation of the automatic alignment apparatus of thethird preferred embodiment of the present invention.

FIG. 15c is a timing diagram of the forward starwheel single stopactuation during the starwheel stop operation of the automatic alignmentapparatus of the third preferred embodiment of the present invention.

FIG. 15d is a timing diagram of the forward starwheel dual stopactuation during the starwheel stop operation of the automatic alignmentapparatus of the third preferred embodiment of the present invention.

FIG. 15e is a timing diagram of the reverse starwheel position duringthe starwheel stop operation of the automatic alignment apparatus of thethird preferred embodiment of the present invention.

FIG. 15f is a timing diagram of the reverse starwheel single stopactuation during the starwheel stop operation of the automatic alignmentapparatus of the third preferred embodiment of the present invention.

FIG. 15g is a timing diagram of the reverse starwheel dual stopactuation during the starwheel stop operation of the automatic alignmentapparatus of the third preferred embodiment of the present invention.

FIG. 16 is a flow diagram of the automatic alignment operation utilizingthe automatic alignment apparatus of the third preferred embodiment ofthe present invention.

FIG. 17 is a schematic view of the rotational runout phenomenonoccurring during a cutting operation of the on-car disc brake lathemounted on the hub of a vehicle.

FIG. 18 is a schematic view of the linear runout phenomenon occurringduring a cutting operation of the on-car disc brake lathe mounted on thehub of a vehicle.

FIGS. 19a and 19b are front and cross-sectional views, respectively, ofa rotary piezo-electric accelerometer of the runout measurement andcontrol system of the of the present invention.

FIG. 20 is a front view of a rotary magnetic hall effect transducer ofthe runout measurement and control system of the of the presentinvention.

FIGS. 21 and 21a are front and side views of a rotary infrared generatoraccelerometer of the runout measurement and control system of the of thepresent invention.

FIG. 22 is a front view of a rotary tuned coil oscillator accelerometerof the runout measurement and control system of the of the presentinvention.

FIG. 23 is a circuit diagram of the control system of the runoutmeasurement and control system of the of the present invention.

DETAILED DESCRIPTION

Context of the Invention

Referring now to FIG. 3, there is shown a perspective view of an on-cardisc brake lathe 30 of the present invention mounted to a hub 44 of avehicle 14 brake assembly. The disc brake lathe 30 includes a motor 32,body 34, cutting head 36 with cutting tools 38, and adapter 40. Thevehicle disc brake assembly includes a rotor 42 operably attached to ahub 44. Typically, the attachment of the rotor 42 to the hub is througha rotor hat (not shown) formed in the rotor 44 (i.e. a "hubless" rotor).However, an integral rotor and hub is occasionally utilized incommercial vehicles. The adapter 40 is mounted to the hub 42 of thevehicle utilizing the lug nuts 46.

Apparatus and Method for Automatic Runout Compensation

The novel on-car disc brake lathe with automatic alignment andcompensation mechanism of the subject invention is now described withreference to FIGS. 4 through 9. Referring to FIG. 4, there is shown alathe 48 having an automatic alignment mechanism 50, lathe housing orbody 52, hub adaptor 54, and drawbar assembly 56. The drawbar assemblyincludes a drawbar 58 that extends through the body 52 and alignmentmechanism 50 and is operably connected to the adaptor 54 by a threadedconnected (as shown) or the like. A calibrate knob 60 is tightenedduring the automated alignment sequence of the lathe and after alignmentis complete, a run knob 62 is tightened for the cutting operation.Spring 64 is a belleville washer that provides a loading force on bar 58which in turn runs through the components of the lathe.

Referring to FIG. 5a there is shown a cross-sectional view of the autoalignment coupling 50 of the preferred embodiment. An input adaptor 66is operably attached to a rotating drive shaft of the lathe machine(shown in phantom in FIG. 4). Shaft 68 is attached to the input adaptor66 such that the adaptor 66 mounting face is perpendicular to the shaft68 axis so that shaft 68 runs true with the lathe machine axis.

Two slant or adjustment disc assemblies 86 and 88 are provided to beinterposed between the input adaptor 66 and an alignment drive disc 70which is attached to the shaft 68 and caused to rotate with it by a key72 and set screw 74. A pivot plate 76 is operably attached to an outputadaptor 78 and mounted to the shaft 68 by spherical bearing 80 so thatthe pivot plate 76 can pivot in relation to shaft 68 while beingconstrained from radial movement.

A pin 82, inserted into pivot plate 76, fits into a slot 84 at theperiphery of the drive disc 70 and causes the pivot plate 76 to berotationally coupled to the shaft 68 and input the adaptor 66. As such,when the input adaptor 66 is mounted on the lathe machine's drive shaftand the output adaptor 78 is mounted on the automobile brake discadaptor 54, the lathe machine output rotation will cause the automobilebrake disc adaptor to rotate, in turn causing the brake disc to rotate.

The slant or adjustment disc assemblies 86 and 88, which are mirrors ofeach other, are placed between the input adaptor 66 and the outputadaptor 78 as shown. The axial force produced by the axially mounteddrawbar 58, that mounts the output adaptor 78 to the automobile brakedisc hub, causes the output adaptor 78 to be forced against slant discassembly 88 and to assume an angle to the shaft 68 that depends upon therelative rotational positions of the slant disc 90 and 92.

Referring to FIG. 6, adjustment disc assemblies 90 and 92 are shown inparallel and in positions of maximum angular runout. Control of therelative position of the slant discs 90 and 92 is accomplished while thelathe machine output shaft is driving the automobile brake disc hub.Specifically, by stopping the rotation of stop disc 94 or 96, itsassociated slant disc is caused to rotate in relation to the other slantdisc, thus producing a change in angle of the output of the adjustmentdisc assemblies 86 and 88, causing the angle of the output adaptor 78 tochange in response. This causes a change in the angular alignment of thelathe machine axis ani the automobile brake disc axis.

As shown in FIGS. 5a and 5b, the stop discs 94 and 96 are selectivelystopped by powering a respective electromagnetic catch 98 and 100. Thecatches are controlled by an microprocessor system that operates inconjunction with a runout measurement and control mechanism described inmore detail below. The lathe machine output shaft rotates at a speedthat is too fast (for example, 123.14 RPM) to allow stop and release ofa stop disc and associated slant disc for adjustment. As such, therotation speed of the adjustment components is slowed by using a geartrain contained in each of the slant disc assemblies. The gear trainwill extend the time permitted for adjustments in a given 1/2 revolutionof the shaft 68 (i.e. the time it takes stop pin 114 to stop therelative rotation of the slant discs in 1/2 revolution for maximumangular runout adjustment). For example, the time will extend at 123.14RPM shaft rotation from 0.243 seconds for 1/2 revolution of the shaft 68to 3.297 seconds thereby permitting easy and complete adjustment of theslant disc assemblies 86 and 88.

Referring to FIGS. 6 and 7a, the preferred gearing mechanism comprises agear 102 containing 88 teeth, and gear 102 is coupled with key 104 torotate with shaft 68. Gear 106 contains 38 teeth and is mounted on apivot 108 formed on stop disc 94. Thus, when stop disc 94 is stopped bythe electromagnetic catch 98, gear 106 rotates at a much faster ratethan shaft 68. For example, if shaft 68 rotates at 123.14 RPM, gear 106rotates at 285.166 . A gear 110, also mounted on pivot 108, is providedwith 36 teeth and is pinned to gear 106 to rotate therewith. Gear 110 iscoupled to a gear 112 that is provided with, for example, 90 teeth. Assuch, gear 112 rotates at 114.06 RPM, or 0.926× the rotational speed ofshaft 68, rotating backwards in relation to shaft 68 and slant disc 92.Because slant disc 90 is pinned to gear 112, it also moves backwards inrelation to shaft 68 thereby adjusting the relative position of theslant discs 90 and 92. The gear arrangement and stop discs of thepresent invention permits the adjustment of the slant disc assemblies,and therefore, the alignment of the lathe drive axis and the hub axis,without the need for a separate motor or power source. It is to beunderstood that the identified gear ratios and rotation speeds arepractical examples and are not intended to limit the scope of theinvention hereof. When the stop disc 94 is released, it and slant disc90, in its new position, again rotates at the rate of the shaft 68.

A stop pin 114 secured to slant disc 92 stops the relative rotation ofthe slant discs at 1/2 revolution, with stop disc 94 being parallel withstop disc 96 at one extreme to maximum angular runout at the otherextreme. Specifically, by stopping the rotation of both stop discs 94and 96, adjustment disc 90 and 92 remain fixed in relation to eachother. Stopping the rotation of stop disc 94 alone until stop pin 114couples to slant disc 90 causes stop disc 96, and thus output adaptor78, to assume the maximum angular runout position.

Referring to FIG. 8, the adjustment disc assemblies 86 and 88 andassociated adjustment discs 90 and 92 are rotated in relation to eachother so that the "slant" or wedge on respective interfaces complementeach other and the input surface of the assembly is parallel with theoutput surface. This is accomplished by stopping the stop disc 94 untilthe pin 114 couples with the slant disc 90. Thus the output adaptor 78"runs true" to the input rotation axis. The angle of the interface ofthe two slant discs has been exaggerated in the figures for clarity. Theangle could be of a dimension that depends on the application of thelathe, but could be in the order of 0.323 degrees. It is noted thatbecause the input adaptor 66 is solidly mounted to the shaft 68 and itsface is perpendicular to the axis of rotation, the adaptor 66 serves asa positioning reference to the slant disc assembly 86. Referring to FIG.9, the slant disc assemblies 86 and 88 with the discs are rotated inrelation to each other by stopping the stop disc 96 until the pin 114couples to the slant disc 90. In this position, the slant angle on thetwo slant discs add to each other causing the output surface of theassembly and the output adaptor 78 to display maximum angular runoutwith the input rotation axis.

With the novel alignment adjustment system of the present invention, therunout caused by a misalignment between the vehicle's hub axis and theaxis of the lathe can be corrected without the time consuming andinaccurate manual methods of the prior art. With the novel system,additional adjustment motors are not necessary and accurate andautomated realignment is possible when the novel alignment system isoperated in conjunction with a measurement and control system of thetype described below.

A second preferred embodiment incorporates the fundamental features ofthose disclosed with respect to the first embodiment, but permitsadjustment with only one slant disc and the output pivots in oneselectable axis only when driven by the slant disc. In the firstpreferred embodiment, the compensation vector (explained in more detailwith reference to FIGS. 11a and 11b) necessary to adjust the angle ofthe output adaptor 78 could potentially require adjustment of two slantdiscs. The fixed pivoting axis of the second preferred embodimenteliminates this problem, requiring only one adjustment, potentiallyreducing the time required for shaft alignment.

Referring to FIG. 10a, there is shown a cross-sectional view of theautomatic alignment coupling or mechanism 120 that occupies the sameposition of the mechanism 50 of the first embodiment shown in FIG. 4.Input adaptor 122 attaches to the rotating shaft of the lathe machine.Shaft 124 is attached to the input adaptor 122 such that the adaptor 122mounting face is perpendicular to the shaft 124 so that shaft 124 runstrue with the lathe machine axis. A second shaft 126 is placed over theshaft 124 and the rotated position of the second shaft 126 relative toshaft 124 is controlled by the stop disc assembly 128. The stop discassembly 128 contains a gear train and operates similarly to the stopdisc assemblies 86 and 88 of the first preferred embodiment. However, inthis case, instead of driving a slant disc when the stop disc 130 isstopped by an electromagnetic catch, the second shaft 126 is driven andmoves backwards relative to the shaft 124. Rotary movement of the shaft126 also controls the rotary position of a pivot ring assembly 132 whichis firmly attached to the second shaft 126. An output adaptor 134 ismounted on the shaft 124, held in place by a clamp ring 136, and causedto rotate with the shaft 124 by a drive disc 138.

A second stop disc assembly 130, containing a gear train, is mounted onthe second shaft 126 and operates similar to stop discs 94 and 96 of thefirst preferred embodiment with the output of the gear train driving asingle slant disc 140 detailed in FIG. 10c. When stop disc 130 isstopped, the slant disc 140 moves backward in relation to shaft 124. Theaxial force produced by an axially mounted drawbar 58, note again FIG.4, causes the output adaptor 134, through the pivot ring 132 to assumean angle to the shaft 124 depending upon the rotated position of slantdisc 140.

Referring to FIG. 10b, there is shown a cross-sectional view ofautomatic alignment mechanism rotated 90 degrees counterclockwise aboutthe input axis of FIG. 10a. The pivot ring 132 does not rest against thestop disc assembly 130 over its entire surface. Rather, there are 2"bumps" diametrically placed on the face of the pivot ring 132 whichrest against the stop disc assembly 130. This allows the slant disc 140to transmit its angle to the pivot ring 132 but allows the pivot ring132 to pivot on its fixed axis pins 142. Thus, once set, thecompensation vector (explained in more detail with reference to FIGS.11a and 11b) necessary for alignment does not change when the slant disc140 varies the output compensation angle. Referring to FIG. 10d, thereis shown the pivot ring assembly 132 in more detail. Specifically, bymaking one of the "bumps" on the pivot ring 132 a certain amount largerthan the other, the pivot ring 132 is made perpendicular to the shaft124 at one extreme position of slant disc 140 and at maximumcompensation angle at the other extreme. A 1/2 degree variance, forexample, is provided between the bumps as shown in FIG. 10d. Similarly,a 1/2 degree variance between the bumps on slant disc 140 is provided asshown in FIG. 10c. Thus, when the slant disc 140 and the pivot ring 132are placed against the disc 130 with the 1/2 degree face anglescomplementing each other, a 0 degree runout between the input to outputadapters is achieved. On the other hand, when the discs are rotated 180degrees relative to each other, the angles oppose each other and therunout input and output is 1 degree.

Referring now to FIGS. 11a and 11b, there is shown a schematic depictingthe relationship between the compensation vector, compensation angle,and pivot axis contemplated by the alignment device of the presentinvention. Generally, two parameters are of importance when aligning therotating shafts of the lathe and brake hub. The first parameter referredto as the "compensation vector" is defined by the a rotation position atwhich the lateral runout deflection of the brake lathe is the greatest.The second parameter referred to as the "compensation angle" is definedby the angle that the input adaptor and the output adaptor must assumein relation to each other in order to compensate for this lateralrunout. In the second embodiment, the compensation vector and thecompensation angle can be adjusted separately as shown in FIG. 10a.

However, in the first and third (described below) embodiments, thecompensation vector is adjusted by "stopping" simultaneously the inputdisc and output disc. This does not affect the relative rotationalpositions of the discs and thus does not change the input to outputangle. Rather, adjustment of the compensation vector only changes therotational position where the disc's angle changing capability iseffective. The compensation angle is adjusted by "stopping" the outputdisc only, which rotates it in relation to the input disc and thuschanges the input to output angle.

Referring now to FIGS. 12 through 16 there is shown a third preferredembodiment of the present invention. The third preferred embodiment issimilar to the first preferred embodiment differing in that the slantdiscs are separated from each other and from the input and outputadapters by pin roller thrust bearings to allow free rotation of theseelements under normal axial pressure; the rotational positioning of theslant discs relative to each other and to the input and output adaptersis performed by actuating four "starwheels" which drive the slant discsthrough gear trains; and both forward and reverse positioning capabilityof the slant discs is provided which allows a considerable decrease intime to final alignment.

Referring to FIG. 12, there is a cross-sectional drawing of an automaticalignment coupling or mechanism 144 that occupies the same position ofthe mechanism 50 of the first embodiment shown in FIG. 4. An inputadaptor 146 attaches to and is rotationally driven by the output shaftof the brake lathe. Adaptor 146 contains two "starwheels" 180 and 182which drive gear trains which ultimately position an input slant disc152, described in more detail with reference to FIG. 13a. An adaptorcover 154 serves as a cover for the gearing and as a bearing surfacewhich runs perpendicularly true to the shaft 156 which is attached toinput adaptor 146.

Thrust bearing assembly 158, with its two race rings, are place betweeninput slant disc 152 and the bearing surface of adaptor cover 154. Thisbearing assembly allows free rotation of the slant disc 152 relative tothe input adaptor 146 and the attached shaft 156 while automaticalignment mechanism is under axial pressure in normal operation. Outputslant disc 160 is separated from slant disc 152 by a thrust bearingassembly 162 identical to thrust bearing assembly 158 to allow outputslant disc 160 to freely rotate under axial pressure. A third thrustbearing assembly 164 is placed between output slant disc 160 and theoutput adaptor cover 166, again to allow free rotation of the outputslant disc 160.

Output adaptor 168 contains the same "starwheel" and gearing assembly asdoes input adaptor 146. It differs in that it is free to move to anangle that varies as much as 1 degree, for example, from perpendicularto the shaft 156 axis. Output adaptor 158 is rotationally coupled to theshaft 156 by means of a drive arm 170 that is keyed to the shaft 156.Referring to FIG. 13b, there is shown the input side of the outputadaptor 168 without the starwheel and gears for clarity. The drive arm170 is shown in place with key 172 coupling it to the shaft 156. A drivepin 174 is positioned in the output adaptor 168 and fits in the slot 176of the drive arm 170 to cause the output adaptor 168 to rotate with theshaft 156 while allowing the output adaptor 168 to tip angularly inrelation to the shaft 156.

Referring to FIG. 12, a collar 178 serves as both a bearing surface forthe inside diameter of output adaptor 168 and a shoulder to prevent thedisassembly of the parts when the auto align mechanism is not operatingunder axial pressure. A wave washer 153 or the like is placed betweeninput slant disc 152 and input adaptor 146 in order to provide somefriction so that rotation of output slant disc 160 will not causeunwanted rotation of the input slant disc 152.

Referring to FIG. 13a, input and output adaptor assemblies preferablycomprise a forward starwheel 180 that is coupled to a gear 184 having,for example, 18 teeth. Gear 184 meshes with a gear 186 having, forexample, 56 teeth. Gear 186 is coupled to gear 188 having, for example,18 teeth. Gear 18 meshes with a ring gear 190 having, for example, 140teeth. The ring gear 190 is operably attached to a respective slant disc152 or 160 as shown in FIG. 12.

Referring again to FIG. 13a, when the entire auto align mechanismrotates at 2.05 RPS, for example, in normal operation, the starwheel 180can be caused to rotate by "catching" one or more teeth as the starwheel180 passes by a fixed stop mechanism comprising an electromagnetic catchor the like. Thus, a slant disc can be caused to rotate in incrementsrelative to the auto align mechanism. The reverse starwheel 182 and gearassembly operates similarly to the forward starwheel 180 and gearassembly except that an additional gear 192 causes the slant disc torotate in the opposite direction when the starwheel 182 is rotated.

Referring to FIG. 14, there is shown starwheel stop mechanism 194 thatcomprises a toothed catch member 196 and a magnetic element such assolenoid 198 or the like. Preferably, one stop mechanism 194 is providedto operate in conjunction with the input adaptor 146 and another isprovided to operate in conjunction with the output adaptor 168. Thetoothed member 196 may contain one or more teeth so as to "catch" one ormore starwheel teeth each rotation of the automatic alignment mechanism.Note that the teeth of the member 196 are spaced apart so as to allowtime to lift the toothed member between starwheel contact to control theamount of starwheel rotation per auto align mechanism rotation.

As the starwheels on each adaptor 146 and 168 are in line, the action ofthe starwheel "catch" or "stop" mechanisms have to be timed insynchronism with the rotation of the auto align mechanism in order thatonly the desired starwheel, (i.e. forward starwheel 180 or reversestarwheel 182) is actuated. FIG. 15 shows an exemplary timing controldiagram for the starwheel stop mechanism 194. As shown, a halltransducer or the like timing pulse is used as a time reference point.

Referring to FIG. 16, there is shown a novel alignment process flowdiagram as specifically exemplified with reference to the thirdpreferred embodiment. It is noted that any suitable measurement devicecould be used in conjunction with the alignment mechanism. Preferably,however, a novel sensing and measuring device of the present inventionas described below is utilized to operate in conjunction with the novelalignment mechanisms described above. It is also noted that although thealignment process is shown and described in FIG. 16 with reference tothe third preferred embodiment, the general process algorithm isapplicable to all embodiments of the present invention. Furthermore, thenovel alignment apparatus and process may also be advantageouslyutilized in other practical applications in order to align twoconcentrically rotating shafts.

In general, the flow diagram of FIG. 16 shows a sequence of "trial anderror" adjustments wherein an adjustment is initially made by stopping astar wheel on one of the adapters and measuring the change in the runoutor alignment. If the runout improved, an additional adjustment isordered in the same direction. If the alignment worsens, an adjustmentin the opposite direction is ordered. This process is repeated until thealignment is corrected to within specifications and the lathe shaft andhub axes are aligned. Two distinct periods of adjustment are employed inthe present invention. A first cycle takes place wherein largeadjustments are made in the orientation of slant discs 152 and 160 tomore significantly chancre the alignment of the shaft and hub axes, andthereby correct runout. Once alignment reaches a predetermined lowlevel, finer adjustments are made to correct runout to within specifiedtolerances.

Referring to FIG. 16, the runout: correction process begins withinitialization of several variables. At step 302, the stop lever of stopmechanism 194 is set to three actuations of the starwheels. Thisprovides the large movements of slant discs 152 and 160 at the beginningof the adjustment cycle. Also at step 302, several internal counts andlimits are initialized including flag Z flag D, and a try counter. Also,the initial specification value is supplied which represents anacceptable level of runout. Typically, this value is set to be in theorder of 0.001 inch. The try counter operates when runout drops to a"Min" value. This counter causes the value of "Spec" to increase afterthe system tries to reach the present "Spec" runout value a programmednumber of tries or cycles. This prevents the system from trying toforever reach a runout value that is impossible given the circumstances.

An initial evaluation of the runout is made at step 303 and thisquantity is stored a R-pres, representative of a base value of therunout. Step 304 provides for a comparison of the measured runout with arunout measurement that conforms to specification, usually on the orderof 0.001 inches as noted above. If the runout is less than 0.001 inches,the runout is determined to fall within specified tolerances ("Spec")and no further compensation is required as is indicated in step 310. Atstep 306, the value of R-pres is copied into the memory location ofR-last. Next, if R-pres does not exceed a predetermined level "Min"(step 307), the stop mechanism 196 is set to stop one tooth of thestarwheel 180 or 182 per revolution as indicated in step 308. At step309, the try count is incremented and at step 310 the try count isevaluated such that of the try count is at a limit, the runout "Spec"limit is raised (step 311) and the try count is reset to 0 (step 312).The higher "Spec" limit usually consist of a value that is stillacceptable but less preferred than the original "Spec" limit (e.g. 0.001inch). For example, 0.003 inch higher "Spec" is acceptable.

At step 313, the flag Z is tested to determine if starwheel actuationhas run in both directions. That is, whether both output 180 (forward)and 182 (reverse) starwheel have been activated. At step) 10, if the Zflag has not been toggled twice, then the program proceeds to step 315to determine the state of flag D and if the Z flag has been toggled hasbeen toggled twice, then step 314 toggles flag D. If D equals 0, thenthe output only starwheel is actuated changing the "compensation angle"of the system. If D equals 1, both the output and input starwheels areactuated to change the "compensation vector" of the system.

At step 318, the system waits for one of two revolutions of the lathe(depending on whether the accelerometer is operating in mode 1 or mode 2as described below) before proceeding in order to allow transientsintroduced by the last starwheel adjustment to dissipate. At step 319,the runout is again measured. In step 320, if runout is less than Spec(e.g. 0.001 or 0.003 inches), the system progresses to step 305 and therunout adjustment is complete. At step 321, the runout from the presentmeasurement, R-pres, is compared to the runout from the lastmeasurement, R-last. If R-pres is less than R-last, the systemprogresses to step 306 where R-pres is copied into R-last and theprocess continues through another iteration and the same starwheelpreviously actuated is again actuated. If, on the other hand, R-pres isgreater than R-last, the system progresses to step 322 where flag Z istoggled to its opposite state. Control is then passed back to step 305where in turn the other starwheel of the starwheel pair is actuated tocause rotation of the adjustment disc in an opposite direction.

In this manner, the system employs a trial and error approach toreducing runout. As long as the runout continues to decrease, additionalactuations of the same starwheel occur. However, if runout worsens, theopposite starwheel is actuated to begin to correct the runout. If thisforward and reverse cycle does not improve the runout, the compensationErector is adjusted by moving both of the input and output adjustmentdiscs. A microprocessor and suitable circuitry controls the operation ofthe present invention as described below with reference to FIG. 23.

The alignment adjustment system of the present invention is asubstantial improvement over prior art devices and techniques. Once theappropriate sensor and measuring system is properly secured (forexample, one of the novel systems disclosed below), the automaticalignment system provides for mechanical compensation of the totallateral runout present in the disc brake assembly. Specifically, thealignment system adjusts the alignment of the brake lathe component withrespect to a vehicle hub in order to compensate for lateral runout.This, in turn, ensures that the cutting head 36 is placed perpendicularto the rotation axis of the hub 44.

Lateral Runout Measurement and Control System

The apparatus and method for runout compensation disclosed above servesto align the lathe and rotor axes under the direction of an angularrunout sensing and control mechanism of the present invention. However,it is to be understood that the runout sensing and control mechanismdescribed herein may be used with any suitable sensor that is responsiveto angular acceleration or variations in the distance between thecutting tool end of the lathe body and the auto under consideration. Inthe present invention, the runout sensor preferable takes the form of anelectronic accelerometer. The novel measurement and control system mayalso be advantageously utilized in other practical applications in orderto align two concentrically attached rotating shafts.

Referring to FIGS. 17 and 18, there is shown a brake lathe assembly,coupled through an auto align mechanism of the type shown and describedabove to a wheel axle. The lathe tools are shown at the end of the brakeassembly mechanism arm, arranged to move from the center of the brakedisc toward the outside while the drive motor causes the wheel and brakedisc to rotate as described above. The solid lines show the mechanismposition when the wheel axis and the lathe axis are in alignment. Underthese conditions the lathe tools cut the disc surfaces smoothly.

However, where runout is present, the lathe will rotate back and forthwhen in use. This dotted lines show the wobbling of the lathe mechanismwhen the wheel axis and the lathe axis are misaligned (in the drawingthe runout is greatly exaggerated). Obviously, with the lathe mechanismand tools wobbling the brake disc lateral runout is cut into the rotorand such operation is not acceptable. Note that at the "X" point themechanism changes its position not only linearly but also in arotational sense perpendicular to the drive axis. That is, the angle ofthe mechanism changes cyclically as the wheel is rotated.

It is at this point that the sensing devices of the runout sensing andcontrol mechanism of the present invention are preferably placed inorder optimize measurement sensitivity. Preferably, the sensing devicesare additionally positioned such that the internal rotor axis (asdescribed below) is perpendicular to the lathe drive axis.

Referring to FIG. 18, there is another misalignment mode which can occurwhen the wheel axis and the lathe axis are in misalignment. This isoff-center misalignment. With this, the motion of the lathe mechanismcontains only linear components while no angular runout occurs,therefore no rotational motion perpendicular to the drive axis occurs.This runout motion does not detract significantly from the smoothcutting of the brake disc surface and can be allowed. For this reason,it is an objective that the sensing device of the present inventionsense only the rotation components impressed upon its housing whilerejecting all linear motions.

A variety of different sensing configurations can be used as a part ofthe runout sensing and control mechanism of the present invention.Generally, there are two operating modes employed in utilizing therotary accelerometer as a runout detector. In a first mode the naturalfrequency of resonant motion of the rotor transducer is configured (asexplained below) to be about 1.5 times the frequency of lathe rotation.In this mode configuration, the accelerometer achieves the most rapidfollowing of the changes in runout and therefore, often the most rapidalignment due to damping inherent in the frequency differential.However, the runout sensitivity of the system is less than 1/2 that ofmode two. In mode two, the natural frequency of resonant motion of therotor-transducer is configured to be below the frequency of latherotation. This provides the most sensitivity to runout and helps tosuppress harmonics in the runout motion which can cause alignmentuncertainty. However, this mode configuration is slower in followingchanges in runout which may slow alignment as compared to modeconfiguration one. In any event, the natural frequency of resonantmotion should never by placed at the frequency of lathe rotation becauseoperating in resonance with the lathe results in an unnatural buildup ofrotor-transducer motion which doesn't allow the accelerometer output toimmediately follow the runout magnitude, seriously slowing the alignmentprocess.

Independent of the operation mode, several considerations are relevantin implementing each of the embodiments of the inventive accelerometer.First, the accelerometer rotor should be completely balanced in order toinsure measurement of rotational accelerations, while rejecting linearaccelerations. Second, the rotation of the rotor should be physicallylimited such that rotation only occurs within the sensitive area of thetransducer. Finally, the natural frequency of resonant motion of therotor-transducer should be configured to operate in either mode 1 or 2as already discussed above. In this regard, the natural frequencydepends on several variable including mass of the rotor, diameter of therotor, and characteristics of a spring element (e.g. music wire).

The accelerometer embodiment using a piezoelectric element as a sensor(described below) is best suited to operating where the naturalfrequency of resonant motion is about 1.5 times the frequency of latherotation because some force is required to bend the element tending tocause a high spring rate. The other transducer schemes described beloware non-contact devices and the spring rate can be dictated by springselection. In this regard, these embodiments are well suited to eithermode one or mode two operation.

In a first embodiment as shown in FIG. 19 there is a rotaryaccelerometer sensor 210. Sensor 210 comprises a housing 212 thatencloses a rotor 214 mounted for rotation on bearings 216 and 218. Therotor 214 is carefully balanced so that all accelerations exceptrotational cause no rotation of the rotor 214. Rotation of the rotor 14is sensed by a piezo electric element 220 which is mounted between thehousing 212 and the rotor 214 and is bent by any rotation of the rotor214 producing a voltage proportional to the magnitude of bending.Rotation of the rotor 214 is limited to protect the piezo electricelement 220 by piezo element mount 220 in the slot 222 in the rotor 214.

The piezo disc 220 and the rotor 214 operate as a spring and mass systemhaving a natural frequency of resonant motion as generally describedabove. In this spring/mass system, the rotor constitutes the mass andthe piezo disc 220 constitutes the spring. In this embodiment, thesystem operates in mode one such that the rotor mass and diameter andthe piezo spring quality is adjusted to obtain a frequency in the orderof 1.5 times the frequency of lathe rotation. It is of furtherimportance that the rotor 11 be suitably damped in order to minimize thesettling time. This can be achieved by filling the housing 10 with aviscous fluid and sealing the housing with a cover. Alternatively,damping can be provided by using a clinging viscous material in thebearings 12 and 13. Other damping techniques are considered to be withinthe scope of the invention. A resultant signal, whose amplitude isproportional to the magnitude of the angular runout, is then directed toa control system as described below with reference to FIG. 23.

The sensing device of the present invention may also be configured withalternative transducing elements that provide a suitable control signal.For example, the inventive sensor may be sensing element comprising anaccelerometer with a tuned coil oscillator. Referring to FIG. 22, thespring component of this system comprises a wire (preferably music orpiano wire) 244 that is attached to the body 256 and rotor 246 as shown.The wire may be attached by any suitable means such as, for example,brackets as shown in FIG. 22. As previously noted, the natural frequencyof resonant motion of the rotor-transducer is dependant on the mass anddiameter of the rotor and spring characteristics. When using a musicwire 244 to control frequency a shown, the tension of the wire 244 andthe wire 244 gage are manipulated to vary the frequency. For example, toachieve a natural frequency or resonant motion of the rotor-transducerthat is below the frequency of lathe rotation, a gage in the range ofapproximately 9-10 thousandths is utilized and the wire tension isconfigured to be relatively loose. On the other hand, to achieve anatural frequency of resonant motion of the rotor-transducer that isabout 1.5 times the frequency of lathe rotation, a gage in the range ofapproximately 16 thousandths is utilized and the wire tension isconfigured to be relatively tight.

A ferrite or the like disc 248 is placed in the periphery of the rotor246 adjacent to a housing-mounted coil 250 which forms the -L- of anoscillator circuit 252. When the rotor 246 turns, the ferrite disc 248moves in relation to the coil 250, causing a change in the inductance ofthe oscillator coil 250, thus a change in the frequency of oscillation.A discriminator 254 converts the change in frequency of oscillation to avarying DC voltage. This varying voltage reflects the rotation of theaccelerometer housing 256. The signal is then forwarded to a controlsystem as described below with reference to FIG. 23.

As previously noted, it is important to configure the rotor such that itis balanced. In order to limit the rotation of the rotor such thatrotation only occurs within the sensitive area of the transducer, acounterbore 245 is provided that cooperates with a pin 247 to limitrotor rotation as appropriate. Other limiting means are within the scopeof the invention.

In an alternative embodiment the sensing device is an accelerometer withan magnet-hall effect transducer as shown in FIG. 20. In thisconfiguration, a leaf spring 222 has a spring rate which, in combinationwith the inertia of the rotor 224, provides a resonant frequency about1.5 times the rotational rate of the brake lathe shaft (i.e. operationin mode one). Alternatively, the accelerometer of this embodiment couldbe configured to operate in mode one or two using a music wire asdescribed above. A magnet 226 is placed in the periphery of the rotor224. A hall effect transducer 228 with a linear characteristic is placedin the housing 230 adjacent to the magnet 226 such that rotary motion ofthe rotor is; reflected in the output voltage of the hall effecttransducer 228. The magnitude of the AC voltage at the output of thehall effect transducer 228 is a reflection of the rotary motion of theaccelerometer housing 230 that is attached to the lathe, preferably atthe position identified with reference to FIGS. 17 and 18. The resultingsignal is forwarded to a control system as described below withreference to FIG. 23.

In yet another alternative embodiment, the sensing element comprises anaccelerometer with an infrared generator. Referring to FIG. 21 and 21a,there is shown a leaf spring 232 that preferably has a spring ratewhich, in combination with the inertia of a rotor 234, provides aresonant frequency about 1.5 times the rotational rate of the brakelathe shaft. Again, this accelerometer could alternatively be configuredto operate in mode one or two using a music wire as described above. Aninfrared generator diode 236 is placed facing an infrared detector diode238 on the housing 240 near the periphery of the rotor 234.

A shutter 242 is attached to the rotor 234 and projects between the IRgenerator 236 and IR detector 238 such that rotary motion of the rotor234 varies the amount of radiant energy transferred, causing the voltageout of the IR detector 238 to reflect the magnitude of housing 240rotation. Again, this measurement reflecting the runout of the disccoupling. The signal is forwarded to a control system as described belowwith reference to FIG. 23.

The runout sensing and control mechanism of the present inventionfurther comprises a control circuit which is now described withreference t) FIG. 23. Transducer 400 may be advantageously comprised ofany of the several different types of sensors designed to evaluate therotational acceleration of the lathe as set forth below. Because lateralrunout manifests itself in varying rotational motion imparted to thelathe, any sensor arrangement capable of producing an accuratequalitative measure of rotational acceleration may be utilized. Thepreferred structured herein utilizes an inertial disc and piezo electricelement as transducer 400, as described in greater detail below. Theoutput of transducer 400 is fed to amplifier 402 and then to rectifier404. Because runout produces a cyclical motion in the lathe, the signalproduced by transducer 400 is sinusoidal in nature; however, at lowerrunout levels other wave forms could resonate. After amplification byamplifier 402 and rectification by full wave rectifier 403, the peakrunout signal is feed to an integrator 404 that is reset 406 each latherotation cycle as indicated. The signal is then sent to a sample andhold circuit 407. A hall pickup timer 405 produces a synchronizationsignal as shown. The output is then transmitted to A/D converter 408which samples the voltage level and produces a digital representationthereof. The output of A/D converter 408 is passed to both latch 410 andmicroprocessor 412. The output of latch 410 is also provided tomicroprocessor 412. Latch 410 is a conventional sample and hold latchand is clocked just prior to the time A/D converter 408 presents a newsample. In this manner, both the current sample taken by A/D converter408 and the last sample taken by A/D converter 408 are available tomicroprocessor 412. At the output of microprocessor 412 there isprovided amplifiers 414 and 416 which are used to drive stop mechanism196.

Taken in conjunction with the algorithm set forth in FIG. 16,microprocessor 412 is thus provided with a stream of samples of therunout of the rotor under consideration, together with a samplerepresenting the last historical value of the runout. In this manner,the microprocessor implements the trial and error approach describedabove with respect to FIG. 16.

SUMMARY OF MAJOR ADVANTAGES OF THE INVENTION

After reading and understanding the foregoing detailed description of aninventive on-car brake lathe with automatic alignment system and processin accordance with preferred embodiments of the invention, it will beappreciated that several distinct advantages of the subject alignmentsystem and process are obtained.

Without attempting to set forth all of the desirable features of theinstant on-car disc brake lathe with automatic alignment system, atleast some of the major advantages include providing an on-car discbrake lathe having an automated alignment assembly 50 that includes apair of adjustment disc assemblies that are positioned between an inputadaptor 66, 122, 146 and an output adaptor 78, 134, 168. Each of theadjustment disc assemblies includes an adjustment disc 90, 92, 140, 152,160 and associated stop disc. An electromagnetic catch 98, 100 or thelike is operably associated with each of the stop discs; 94, 96 andoperates in response to a control signal issued from a control system.When the rotation of one of the stop discs is stopped, rotationalmovement of the lathe drive shaft is transferred, through appropriategearing, to a respective adjustment disc to change the relative positionof the lathe drive axis and the vehicle hub axis.

In a preferred embodiment, the control algorithm and alignment processof the present comprises a series of "trial and error" adjustmentinquiries in order to compensate for runout. As the lathe begins torotate and the Hall signal provides a timing signal, and the runoutlevel is evaluated and if within the "Spec" limit, normally 0.001", thealignment goes to the "Low-Ready to Cut" light and the program ends. Ifthe runout is above the "Spec" limit, an actuation of the output forwardstarwheel is ordered. The runout is evaluated and if lower, addedactuations of the same starwheel are ordered until an actuation causesthe runout to increase. At this point, if the runout is still above the"Spec" limit, an actuation of the output reverse starwheel is ordered.If the runout is lower, further such actuations are ordered until anactuation causes the runout to increase. The previous two actionsadjusts the "compensation angle." At this point, if the runout is stillabove tae "Spec" limit, an actuation of both the output and the inputforward starwheels in tandem is ordered. This action adjusts the"compensation vector." The runout is evaluated and if lower, furtheractuations of the output and input forward starwheels in tandem areordered until an actuation causes the runout to increase.

At this point, if the runout is still above the "Spec", an actuation ofthe output and input reverse starwheels in tandem is ordered. The runoutis evaluated and if lower, further such actuations are ordered. If anactuation causes a runout increase, and if the runout is still above the"Spec" limit, the starwheel actuations revert to the output starwheelsonly mode again as described previously. This actuation sequencecontinues as above, trial and error, until the runout is reduced to the"Spec" limit, where the "Ready to Cut" light is illuminated and theprogram ceases.

A count is kept of the number of tries to reach the "Spec" runout leveland when a preset number of tries is exceeded, the acceptance level israised to about 0.0031" and if the runout is within this level, a "Readyto Cut" light is illuminated and the program ceases. If this new higherrunout level can not be reached after a preset number of tries, a "Outof Spec" lite is illuminated and the program ceases. The operator isdirected to check the lathe coupling to the brake disc hub and to checkfor bad wheel bearings, correct the problem and try the alignment cycleagain. Depending on the level of runout, the system can be controlledsuch that 3 starwheel teeth are "caught" in each starwheel actuation forrapid adjustment or only 1 starwheel tooth is caught each actuationallowing fine adjustment of the runout level.

In describing the invention, reference has been made to a preferredembodiment and illustrative advantages of the invention. Those skilledin the art, however, and familiar with the instant disclosure of thesubject invention, may recognize additions, deletions, modifications,substitutions and other changes which fall within the purview of thesubject invention.

What is claimed:
 1. An on-vehicle disc brake lathe system forresurfacing a brake disc of a vehicle brake assembly, the brake lathesystem comprising a lathe body with a driving motor, a cutting headoperably attached to the lathe body, and a drive shaft, the on-vehiclebrake lathe system being further defined by an alignment systemcomprising:a sensor operable to produce a signal indicative of movementof the lathe body; an electronic controller operable to receive thesignal from the sensor and to use the signal in generating at least onecontrol signal; an input adaptor attached to the drive shaft to rotatewith the drive shaft; a hub adaptor configured to attach to a hub of avehicle and to rotate with the drive shaft; and an adjustment mechanismcoupled to the input adaptor, responsive to the at least one controlsignal from the electronic controller, and operable to automaticallyadjust an axial alignment of the input adaptor with respect to an axisof rotation of the hub adaptor in response to the at least one controlsignal from the electronic controller, wherein the electronic controllergenerates the at least one control signal so that automaticallyadjusting the axial alignment reduces movement of the lathe body so asto improve alignment of the lathe body and the cutting head relative toan axis of rotation of the hub of the vehicle.
 2. The on-vehicle discbrake lathe system of claim 1, further comprising:a draw bar extendingthrough the lathe body and the input adaptor and connected to the hubadaptor.
 3. The on-vehicle disc brake lathe system of claim 1, whereinthe adjustment mechanism is powered by rotation of the drive shaft. 4.The assembly of claim 1, wherein the adjustment mechanism is powered byrotation of the input adaptor.
 5. The on-vehicle disc brake lathe systemof claim 1, wherein the adjustment mechanism comprises:at least one stopdisc coupled to the input adaptor and operable to selectively follow therotation of the drive shaft or to rotate relative to the drive shaft inresponse to the at least one control signal from the electroniccontroller.
 6. The on-vehicle disc brake lathe system of claim 5,wherein the adjustment mechanism further comprises:at least oneadjustment component associated with the stop disc and operable torotate in response to the relative rotation of the stop disc, wherein anaxial alignment of the input adaptor relative to the hub adaptor variesbased on a rotational orientation of the adjustment component.
 7. Theon-vehicle disc brake lathe system of claim 5, wherein the adjustmentmechanism further comprises:at least one stop mechanism associated withthe stop disc, the stop mechanism being operable to move between a firstposition in which the stop disc rotates relative to the drive shaft anda second position in which the stop disc follows the rotation of thedrive shaft, the stop mechanism moving between the first and secondpositions in response to the at least one control signal from theelectronic controller.
 8. The on-vehicle disc brake lathe system ofclaim 7, wherein the stop mechanism comprises an electromagnetic elementand a catch member operable to move from the second position to thefirst position in response to the at least one control signal.
 9. Theon-vehicle disc brake lathe system of claim 8, wherein the at least onestop disc comprises at least two stop discs rotatably secured to theinput adaptor such that the stop discs follow the rotation of the inputadaptor when the stop mechanism is in the second position and at leastone of the stop discs rotates relative to the input adaptor when thestop mechanism is in the first position.
 10. The on-vehicle disc brakelathe system of claim 8, wherein the adjustment mechanism furthercomprises:a first adjustment component associated with a first stop discand operable to rotate in response to the relative rotation of the firststop disc, and a second adjustment component associated with a secondstop disc and operable to rotate in response to the relative rotation ofthe second stop disc, wherein an axial alignment of the input adaptorrelative to the hub adaptor varies based on rotational orientations ofthe first and second adjustment components.
 11. The on-vehicle discbrake lathe system of claim 10, wherein the first and second adjustmentcomponents comprise slant discs, each having a slanted surface such thatthe slanted surfaces of the slant discs are opposed to each other in anabutting relationship.
 12. The on-vehicle disc brake lathe system ofclaim 10, further comprising:a first gear train operably associated withthe first stop disc and the first adjustment component, and a secondgear train operably associated with the second stop disc and the secondadjustment component, wherein each gear train is configured to followthe movement of the corresponding stop disc to move the correspondingadjustment component.
 13. The on-vehicle disc brake lathe system ofclaim 7, wherein the at least one stop disc comprises a starwheel havinga plurality of protruding teeth.
 14. The on-vehicle disc brake lathesystem of claim 13, wherein the stop mechanism comprises anelectromagnetic element and a catch member operable to move from thesecond position to the first position to engage at least one of theplurality of teeth of the starwheel.
 15. The on-vehicle disc brake lathesystem of claim 14, further comprising at least a second stop disc,wherein the electronic controller is operable to control generation ofthe at least one control signal to time the actuation of the stopmechanism such that the catch member moves into the first position at atime appropriate to contact a specified one of the stop discs.
 16. Theon-vehicle disc brake lathe system of claim 15, further comprising anorientation sensor operable to produce an orientation signal indicativeof a rotational orientation of the input adaptor, wherein the electroniccontroller is connected to receive the orientation signal and to use theorientation signal in controlling generation of the at least one controlsignal.
 17. The on-vehicle disc brake lathe system of claim 5, whereinthe at least one stop disc comprises a starwheel having a plurality ofprotruding teeth.
 18. The on-vehicle disc brake lathe system of claim 5,wherein the at least one stop disc has an axis of rotation that isoffset from an axis of rotation of the input adaptor.
 19. An on-vehicledisc brake lathe system for resurfacing a brake disc of a vehicle brakeassembly, the brake lathe system comprising a lathe body with a drivingmotor, a cutting head operably attached to the lathe body, and a driveshaft, the on-vehicle brake lathe system being further defined by analignment system comprising:an electronic controller operable to produceat least one control signal; an input adaptor attached to the driveshaft to rotate with the drive shaft; a hub adaptor configured to attachto a hub of a vehicle and to rotate with the drive shaft; and anadjustment mechanism coupled to the input adaptor, responsive to the atleast one control signal from the electronic controller, and operable toautomatically adjust an axial alignment of the input adaptor withrespect to an axis of rotation of the hub adaptor in response to the atleast one control signal from the electronic controller, wherein theadjustment mechanism comprises:at least one stop disc coupled to theinput adaptor and operable to selectively follow the rotation of thedrive shaft or to rotate relative to the drive shaft in response to theat least one control signal from the electronic controller, and at leastone adjustment disc associated with the stop disc and operable to rotatein response to the relative rotation of the stop disc, wherein an axialalignment of the input adaptor relative to the hub adaptor varies basedon a rotational orientation of the adjustment disc.
 20. The on-vehicledisc brake lathe system of claim 19, wherein the adjustment mechanismfurther comprises:at least one stop mechanism associated with the stopdisc, the stop mechanism being operable to move between a first positionin which the stop disc rotates relative to the drive shaft and a secondposition in which the stop disc follows the rotation of the drive shaft,the stop mechanism moving between the firs and second positions inresponse to the at least one control signal from the electroniccontroller.
 21. The on-vehicle disc brake lathe system of claim 20,wherein the at least one stop disc comprises a starwheel having aplurality of protruding teeth.
 22. The on-vehicle disc brake lathesystem of claim 21, wherein the stop mechanism comprises anelectromagnetic element and a catch member operable to move from thesecond position to the first position to engage at least one of theplurality of teeth of the starwheel.
 23. The on-vehicle disc brake lathesystem of claim 22, further comprising at least a second stop disc,wherein the electronic controller is operable to control generation ofthe at least one control signal to time the actuation of the stopmechanism such that the catch member moves into the first position at atime appropriate to contact a specified one of the stop discs.
 24. Theon-vehicle disc brake lathe system of claim 20, wherein:the at least onestop disc comprises a pair of stop) discs rotatably secured to the inputadaptor such that the pair of stop discs follow the rotation of theinput adaptor when the stop mechanism is in the second position and atleast one of the pair of stop discs rotates relative to the inputadaptor when the stop mechanism is in the first position.
 25. Theon-vehicle disc brake lathe system of claim 24, wherein:the alignmentsystem further comprises an output adaptor coupled to the drive shaftand having a face contacting the hub adaptor; the adjustment mechanismfurther comprises a second stop mechanism operable to move between afirst position and a second position in response to the at least onecontrol signal from the electronic controller; and the at least one stopdisc comprises a further pair of stop discs rotatably secured to theoutput adaptor such that the further pair of stop discs follow therotation of the output adaptor when the second stop mechanism is in thesecond position and at least one of the further pair of stop discsrotates relative to the output adaptor when the associated stopmechanism is in the first position.
 26. The on-vehicle disc brake lathesystem of claim 25, wherein:the at least one adjustment disc comprises afirst adjustment disc operably associated with the pair of stop discsand a second adjustment disc operably associated with the further pairof stop discs.
 27. The on-vehicle disc brake lathe system of claim 26,further comprising:a first gear train operably associated with the pairof stop discs and a second gear train operably associated with thefurther pair of stop discs, the gear trains configured to follow themovement of the respective pair of stop discs, the first gear trainbeing operably associated with the first adjustment disc and the secondgear train being operably associated with the second adjustment disc.28. The on-vehicle disc brake lathe system of claim 27, wherein thefirst and second gear trains are configured such that when one of thefirst and second stop mechanisms stops one of the respective pair ofstop discs, the respective adjustment disc is caused to rotate in afirst rotational direction and when the stop mechanism stops the otherof the respective pair of stop discs, the respective adjustment disc iscaused to rotate in a rotational direction opposite to the firstrotational direction.
 29. The on-vehicle disc brake lathe system ofclaim 28, further comprising:a ring gear operably connected to the firstslant disc such that movement of the ring gear is followed by the slantdisc.
 30. The on-vehicle disc brake lathe system of claim 26,wherein:the first and second adjustment discs comprise slant discs, eachhaving a slanted surface such that the slanted surfaces of the slantdiscs are opposed to each other in an abutting relationship.
 31. Theon-vehicle disc brake lathe system of claim 26, further comprising agear train, the gear train comprising a first gear section associatedwith one of the pair of stop discs and a second gear section associatedwith the other of the stop discs, wherein:the first gear sectioncomprises a first gear element operable to rotate with a respective stopdisc, a second gear element meshed with the first gear element, and athird gear element operable to rotate with the second gear element, thethird gear element being meshed with the ring gear such that rotation ofthe associated stop disc causes respective rotation of the first,second, and third gear elements thereby causing rotation of the ringgear in the first rotational directional; the second gear sectioncomprises a first gear element operable to rotate with a respective stopdisc, a second gear element meshed with the first gear element, and athird gear element meshed with the second gear element, and fourth gearelement operable to rotate with the third gear element, the fourth gearelement being meshed with the ring gear such that rotation of theassociated stop disc causes respective rotation of the first, second,third, and fourth gear elements thereby causing rotation of the ringgear in a rotational direction opposite the first rotationaldirectional.
 32. The on-vehicle disc brake lathe system of claim 31,further comprising a drive arm keyed to rotate with the drive shaft, thedrive arm rotationally coupled to the output adaptor such that theoutput adaptor follows the rotation of the drive arm, the output adaptorfurther configured to be capable of rotating about a vertical axisperpendicular to the central axis of the drive shaft.
 33. An automaticalignment assembly for use in an on-vehicle disc brake lathe system forresurfacing a brake disc of a vehicle brake assembly, the alignmentsystem comprising:an electronic controller operable to generate at leastone control signal; an input adaptor configured to rotate with a driveshaft of a brake lathe system; a hub adaptor configured to attach to ahub of a vehicle and to rotate with the drive shaft; and an adjustmentmechanism coupled to the input adaptor, responsive to the at least onecontrol signal from the electronic controller, and operable toautomatically adjust an axial alignment of the input adaptor with thehub adaptor in response to the at least one control signal from theelectronic controller, wherein the adjustment mechanism comprises:atleast one stop disc coupled to the input adaptor and operable toselectively follow the rotation of the input adaptor or to rotaterelative to the input adaptor in response to the at least one controlsignal from the electronic controller, and at least one adjustment discassociated with the stop disc and operable to rotate in response to therelative rotation of the stop disc, wherein an axial alignment of theinput adaptor relative to the hub adaptor varies based on a rotationalorientation of the adjustment disc.
 34. The assembly of claim 33,wherein:the at least one stop disc comprises a pair of step discsrotatably secured to the input adaptor such that the pair of stop discsrotate with the input adaptor and, under certain predeterminedconditions, rotate relative to the input adaptor.
 35. The assembly ofclaim 34, wherein:the alignment system further comprises an outputadaptor coupled to the drive shaft and having a face contacting the hubadaptor; the adjustment mechanism further comprises a second stopmechanism operable to move between a first position and a secondposition in response to the at least one control signal from theelectronic controller; and the at least one stop disc comprises afurther pair of stop discs rotatably secured to the output adaptor suchthat the further pair of stop discs rotate with the output adaptor and,under certain predetermined conditions, rotate relative to the outputadaptor.
 36. The assembly of claim 35, wherein:the at least oneadjustment disc comprises a first adjustment disc operably associatedwith the pair of stop discs and a second adjustment (disc operablyassociated with the further pair of stop discs, and the first and secondadjustment discs comprise slant discs, each having a slanted surfacesuch that the slanted surfaces of the slant discs are opposed to eachother in an abutting relationship.
 37. The assembly of claim 36, furthercomprising:a first gear train operably associated with the pair of stopdiscs and a second gear train operably associated with the further pairof stop discs, the gear trains configured to follow the movement of therespective pair of stop discs, the first gear train being operablyassociated with the first adjustment disc and the second gear trainbeing operably associated with the second adjustment disc.
 38. Theassembly of claim 37, further comprising:a first adaptor cover adjacentto the input adaptor and a second adaptor cover adjacent the outputadaptor, the input and output adaptors, adaptor covers, and adjustmentdiscs having a concentric axis of rotation.
 39. The assembly of claim38, further comprising:thrust bearings positioned between surfaces ofthe input and output adaptors and adjacent surfaces of the adjustmentdiscs.
 40. An apparatus for automatically aligning the axes of tworotating shafts, the apparatus comprising:an electronic controller; aninput adaptor attached to a first shaft to rotate with the first shaft;an output adaptor attached to a second shaft to rotate with the secondshaft; an adjustment mechanism coupled to the input adaptor, responsiveto the at least one control signal from the electronic controller, andoperable to automatically adjust an axial alignment of the first shaftwith respect to an axis of rotation of the second shaft in response tothe at least one control signal from the electronic controller; and asensor operable to produce a signal indicative of movement of acomponent coupled to the input adaptor; wherein the electroniccontroller is connected to receive the signal from the sensor andoperable to use the signal from the sensor in producing the at least onecontrol signal so as to adjust the axial alignment to reduce movement ofthe component coupled to the input adaptor.
 41. The apparatus of claim40, wherein the adjustment mechanism is powdered by rotation of theinput adaptor.
 42. An on-vehicle disc brake lathe system for resurfacinga brake disc of a vehicle brake assembly, the brake lathe systemcomprising a lathe body with a driving motor, a cutting head operablyattached to the lathe body, and a drive shaft, the on-vehicle brakelathe system being further defined by an alignment system comprising:anelectronic controller operable to generate at least one control signal;an input adaptor attached to the drive shaft to rotate with the driveshaft; a hub adaptor configured to attach to a hub of a vehicle and torotate with the drive shaft; an adjustment mechanism coupled to theinput adaptor, responsive to the at least one control signal from theelectronic controller, and operable to automatically adjust an axialalignment of the input adaptor with respect to an axis of rotation ofthe hub adaptor in response to the at least one control signal from theelectronic controller; and a sensor for measuring lateral runout of thelathe system, the sensor providing an electrical measurement signal tothe electronic controller, and the electronic controller using themeasurement signal to generate the at least one control signal providedto the adjustment mechanism.
 43. The on-vehicle disc brake lathe systemof claim 42, wherein the adjustment mechanism comprises:at least onestop disc coupled to the input adaptor and operable to selectivelyfollow the rotation of the drive shaft or to rotate relative to thedrive shaft in response to the at least one control signal from theelectronic controller.
 44. The on-vehicle disc brake lathe system ofclaim 43, wherein the adjustment mechanism further comprises:at leastone adjustment component associated with the stop disc and operable torotate in response to the relative rotation of the stop disc, wherein anaxial alignment of the input adaptor relative to the hub adaptor variesbased on a rotational orientation of the adjustment component.
 45. Theon-vehicle disc brake lathe system of claim 44, wherein the adjustmentmechanism further comprises:at least one stop mechanism associated withthe stop disc, the stop mechanism being operable to move between a firstposition in which the stop disc rotates relative to the drive shaft anda second position in which the stop disc follows the rotation of thedrive shaft, the stop mechanism moving between the first and secondpositions in response to the at least one control signal from theelectronic controller.
 46. The on-vehicle disc brake lathe system ofclaim 45, wherein the stop mechanism comprises an electromagneticelement and a catch member operable to move from the second position tothe first position in response to the at least one control signal. 47.The on-vehicle disc brake lathe system of claim 46, wherein the at leastone stop disc comprises at least two stop discs rotatably secured to theinput adaptor such that the stop discs follow the rotation of the inputadaptor when the stop mechanism is in the second position and at leastone of the stop discs rotates relative to the input adaptor when thestop mechanism is in the first position.
 48. The on-vehicle disc brakelathe system of claim 46, wherein the adjustment mechanism furthercomprises:a first adjustment component associated with a first stop discand operable to rotate in response to the relative rotation of the firststop disc, and a second adjustment component associated with a secondstop disc and operable to rotate in response to the relative rotation ofthe second stop disc, wherein an axial alignment of the input adaptorrelative to the hub adaptor varies based on rotational orientations ofthe first and second adjustment components.
 49. The on-vehicle discbrake lathe system of claim 48, wherein the first and second adjustmentcomponents comprise slant discs, each having a slanted surface such thatthe slanted surfaces of the slant discs are opposed to each other in anabutting relationship.
 50. The on-vehicle disc brake lathe system ofclaim 48, further comprising:a first gear train operably associated withthe first stop disc and the first adjustment component, and a secondgear train operably associated with the second stop disc and the secondadjustment component, wherein each gear train is configured to followthe movement of the corresponding stop disc to move the correspondingadjustment component.
 51. The on-vehicle disc brake lathe system ofclaim 45, wherein the at least one stop disc comprises a starwheelhaving a plurality of protruding teeth.
 52. The on-vehicle disc brakelathe system of claim 51, wherein the stop mechanism comprises anelectromagnetic element and a catch member operable to move from thesecond position to the first position to engage at least one of theplurality of teeth of the starwheel.
 53. The on-vehicle disc brake lathesystem of claim 52, further comprising at least a second stop disc,wherein the electronic controller is operable to control generation ofthe at least one control signal to time the actuation of the stopmechanism such that the catch member moves into the first position at atime appropriate to contact a specified one of the stop discs.
 54. Theon-vehicle disc brake lathe system of claim 53, further comprising anorientation sensor operable to produce an orientation signal indicativeof a rotational orientation of the input adaptor, wherein the electroniccontroller is connected to receive the orientation signal and to use theorientation signal in controlling generation of the at least one controlsignal.
 55. The on-vehicle disc brake lathe system of claim 43, whereinthe at least one stop disc comprises a starwheel having a plurality ofprotruding teeth.
 56. The on-vehicle disc brake lathe system of claim43, wherein the at least one stop disc has an axis of rotation that isoffset from an axis of rotation of the input adaptor.
 57. An automaticalignment assembly for use in an on-vehicle disc brake lathe system forresurfacing a brake disc of a vehicle brake assembly, the alignmentsystem comprising:a sensor operable to produce a signal indicative ofmovement of a lathe body of the brake lathe system; an electroniccontroller responsive to the signal from the sensor and operable to usethe signal in generating at least one control signal; an input adaptorconfigured to be rotated with a drive shaft of a brake lathe system; ahub adaptor configured to attach to a hub of a vehicle and to rotatewith the drive shaft; and an adjustment mechanism coupled to the inputadaptor, responsive to the at least one control signal from theelectronic controller, and operable to automatically adjust an axialalignment of the input adaptor with the hub adaptor in response to theat least one control signal from the electronic controller.